Integrating a Comprehensive Analytical Approach for Toxic-Load Assessment in Urban Wastewater: Implications for Data-Driven Regulation

Abstract Extensive monitoring of organic pollutants in urban wastewater is mandated by Directive (EU) 2024/3019, yet discrepancies between regulatory prioritization and scientific evidence remain. This study aims to comprehensively characterize the chemical and toxic composition of wastewater from two sites subjected to different anthropogenic pressures. To achieve this, a combined analytical strategy integrating target analysis with semi-quantitative suspect screening was applied, extending beyond current regulatory requirements. The results revealed complex mixtures of organic pollutants across multiple chemical classes in both wastewater treatment plants, with distinct chemical fingerprints reflecting location-specific human activities. Suspect screening substantially expanded (+23%) chemical coverage, identifying 90 previously overlooked contaminants. Instead of counting compounds exceeding their PNEC, compounds and chemical classes were ranked by their contribution to the cumulative toxic load, preserving each compound’s quantitative contribution to overall mixture toxicity. Toxic-load assessment showed that increased chemical complexity does not necessarily correspond to higher toxic pressure, as overall toxicity was driven by a limited number of high-impact substances. The study introduces a robust, holistic, and novel approach for next-generation, integrated target and suspect screening-based monitoring of urban wastewater and mixture toxic-load assessment for compounds identified in effluent wastewater.